In a typical top cored engine block construction, the cylinder tubes formed therein are substantially independent of the surrounding block structure, except for the attachment of each tube to the base, or floor, section of the surrounding cooling jacket. The block, including the cylinder tubes as well as the walls and floor section forming the cooling jacket therefor, is normally a one-piece casting. Heretofore, when machining and boring such a block, the compliance of the free-standing cylinder tubes caused serious cantilever and ring-type distortions. In an efford to reduce the seriousness of such distortions, radially extending stiffening supports (sometimes referred to as webs or struts) were frequently incorporated in the block which extended from the exterior of the tubes to head bolt bosses, the latter being located in close proximity to the tubes. Such supports were normally short and relatively thick and, thus, were very stiff or rigid in both the vertical and radial directions. Furthermore, the configuration of such supports oftentimes seriously impeded flow of the coolant through the cooling jacket which in turn impaired efficient operation of the engine.
Because of the stiffness of the supports, particularly in the vertical (axial) direction relative to the tubes, substantial distortions nevertheless developed in the tube walls when the cylinder head was drawn up tight on the top surface of the block to produce the necessary combustion seal for each of the engine cylinders. Because of such distortions, distribution of the seal load could not be uniformly effected.
Besides the shortcomings associated with the stiffness of the radial supports, oftentimes the locations of such supports relative to the exterior of the cylinder tubes did not effectively impede outward distortion of the tube wall in the area where the greatest internal pressure was generated during operation of the engine. By reason of this latter distortion, which normally occurred in the vicinity of the top combustion ring of the piston head when the latter was disposed at its top dead center, fretting and wear of the combustion seal by the cylinder tubes was increased thereby significantly shortening the useful life of such seal.